Two years ago, sonar images revealed strange circles at the bottom of Lake Michigan that scientists couldn't explain. Now, a survey has determined the shapes are giant holes — but there are many more secrets left to unravel, researchers say.
The holes were first discovered in 2022, when researchers embarked on a mission to map the lakebed inside the Wisconsin Shipwreck Coast National Marine Sanctuary, a protected area of Lake Michigan that contains 36 known shipwrecks, and may contain many more. Weird circles appeared on the map that looked natural rather than human-made, Russ Green, a maritime archaeologist and superintendent of the sanctuary who took part in the mapping project, told Live Science in an email. The shapes were likely depressions in the lakebed, but the researchers couldn't be sure.
